Process for producing a protective color film on an aluminum substrate

ABSTRACT

A process is disclosed for producing a firmly adhered colored film on an aluminum substrate without anodization. The process is carried out at certain temperatures and in the presence of specified quantities of organic amines which amines act to cause a coating to adhere intimately to the aluminum surface and impart a clear amber color to the coating.

nite States Tagai et a1.

[451 Jan. 22, 1974 [76] Inventors: Hideo Tagai, No. 4-1 Denen Chofu, Ohta-ku, Tokyo; Toshiro Takahashi, No. 2-100 Magarigane, Shizuokashi, Shizuoka-ken; Toshihiro Nagano, No. 2-100 Magarigane, Shizuoka-shi, Shizuoka-ken; Matsuo Suzuki, No. 2-100 Magarigane, Shizuoka-shi, ShiZuoka-ken; Katsushige Ikeda, No. 2-3 89 Nishi Awaji-cho, Higashi Yodogawa, Osaka-shi, Osaka-fu; Takashi Kato, No. 2-389 Nishi Awaji-cho, l-ligashi Yodogawa, Osaka-shi, Osaka-fu; Nobuo Minagawa, No. 2-389 Nishi Awaji-cho, l-ligashi Yodogawa, Osaka-shi; Osaka-fu, all of Japan [22] Filed: July 6, 1971 [21] Appl. No.: 160,110

[ Foreign Application Priority Data July 7, 1970 Japan 445-59267 [52] US. Cl l48/6.27, 117/75, 117/132 B, 117/161 R, 148/13.1

[51] llnt. Cl. C23f 7/06 [58] Field of Search..... 148/6, 6.27, 13.1, 6.2, 31.5; 117/132 BF, 70, 72, 75, 49, 62.1, 128.4,127,

132 R, 132 B, 161 R Primary ExaminerAlfred L. Leavitt Assistant ExaminerFrank Frisenda Attorney, Agent, or Firm-Bucknam & Archer [5 7 ABSTRACT A process is disclosed for producing a firmly adhered colored film on an aluminum substrate without anodization. The process is carried out at certain temperatures and in the presence of specified quantities of organic amines which amines act to cause a coating to adhere intimately to the aluminum surface and impart a clear amber color to the coating.

4 Claims, No Drawings PROCESS F OR PRODUCING A PROTECTIVE COLOR FILM ON AN ALUMINUM SUBSTRATE This invention relates to a process of producing on an aluminum surface a protective, ornamental film. More specifically, the present invention is concerned with the process in which an aluminum substrate is coated by immersion-deposit with a continuous, smooth and firmly adhered resinous film. Yet more specifically, the invention is concerned with the aluminum surface treatment in which there is provided on an aluminum surface an attractively colored coating without addition of any coloring dyes or chemicals.

A variety of processes have hitherto been proposed for providing a protective colored film on aluminumbearing substrates. Typical prior-art examples are summarized below.

1. An aluminum substrate is subjected to anodization in an electrolyte bath to provide a porous oxidized film on the aluminum surface. To the porous surface is ap plied an organic dye or otherwise coloring metal or metal oxide. The aluminum is thereafter treated to fill in the pores on its surface and/or finished with a transparent coating.

2. Anodized aluminum surface is coated with a color paint.

3. Various coloring chemicals are introduced into an electrolyte bath for anodizing an aluminum surface, so that there is produced on the surface a colored oxidized film. The anodized aluminum is treated to seal its porous surface and/or finished with a transparent coating.

4. Aluminum is alloyed with different colorproducing metals and anodized. The anodized aluminum alloy is subjected to porosity-sealing treatment and/or finished with a transparent coating.

5. Aluminum substrate is immersed in a bath containing various kinds of chemicals thereby chemically forming a colored oxidized film on its surface. The aluminum surface is finished with a transparent coating.

6. Color paints are applied directly onto an aluminium surface.

The foregoing processes 1 through 4, inclusive, rely on the anodization which necessarily requires costly facilities and which further involves additional colorproducing, porosity-sealing and finish-coating operations. The process 5 of prior-art is not satisfactory in that the film formed on the aluminum surface is rather soft and hence requires additional protective coating, yet is easy to strip apart from the aluminum surface. Again, the above-noted processes 2 through 5, inclusive, have the disadvantage that irregularities are found in the finished color and that skin characteristics of aluminum are lost. Anodization has been necessary prior to a final resin coating step, in the processes of the prior art, for the purpose of obtaining afirmly adherent resinous overcoat.

It is the primary object of the present invention to provide a novel process for producing a protective, colored film on an aluminum surface, which process will eliminate the foregoing difficulties of the various priorart processes.

It is a more specific object of the invention to provide a novel process which is capable of producing on an aluminum substrate a colored under-coat and a resinous over-coat simultaneously without resort to conventional anodization treatment.

We have discovered that an aluminum surface turns clear amber in color owing to the formation thereon of a boehmite or bayerite film under certain treatment conditions. We have also ascertained that a boehmite or bayerite film resulting from the immersion of an aluminum substrate in an amine-containing solution enhances adhesion of the coating composition to the aluminum surface. These discoveries are based upon the various known facts that the formation of a boehmite film on an aluminum surface is promoted when the aluminum is cooked. at certain temperature in a solution containing an organic amine or ammonium; an aluminum surface turns from grey to black in color when the aluminum is treated for boehmite formation in a boiling water containing silicic acid or sodium hydroxide; and an aluminum surface when treated with water heated at about C grows coarse, evidencing the formation thereon of a dark grey bayerite film.

Now, a preferred process according to the invention essentially comprises cleaning an aluminum substrate with warm dilute caustic soda, immersing the aluminum for at least 5 minutes in distilled water or desalted water containing 0.1 10 percent of an organic amine selected from the group consisting of dimethylethanolamine, monoethanolamine, triethanolamine, mono-normal-propylamine, tetraethylenepentamine and ethylenediamine, heated at 4090C., immersing said aluminum in a coating composition comprising 20-50 percent of one or more of water-soluble thermosetting resins selected from the group consisting of acrylic, alkyd, melamine, phenolic, urea and aminoalkyd resins and 0.1-10 percent of said organic amine and maintained at room temperature, and allowing the thus coated aluminum surfaces to set, dry and harden at l50200C over a period of 15-30 minutes.

An alternative process of the invention comprises cleaning a starting aluminum substrate with warm dilute caustic soda, immersing the aluminum at least for 5 minutes in a coating composition comprising 20-50 percent of one or more of water-soluble thermosetting resins selected from the group consisting of acrylic, alkyd, melamine, phenolic, urea and aminoalkyd resins and 0.1-l0 percent of an organic amine selected from the group consisting of dimethylethanolamine, monoethanolamine, triethanolamine, mono-normalpropylamine, tetraethylenepentamine and ethylenediamine and heated at 40 C and allowing the thus coated aluminum surfaces to set, dry and harden at l50200C over a period of 15-30 minutes.

Repeated experiments have indicated that there is no appreciable difference in the quality or adhesive strength of the colored film which is obtained by either of the two processes described above.

Although the reason for the phenomenon is not precisely known, the amber color produced on treated aluminum surfaces is believed to be attributable to the fact that the boehmite or bayerite layer is partially reduced by amine and deposits itself in infinitesimally small particles on the aluminum surface, which particles absorb certain selected spectrum.

The following examples are provided to further illustrate the process of the present invention, but these are not to be regarded as limiting.

EXAMPLE I An aluminum workpiece was dipped in a 10 percent caustic soda solution heated at 70C to dissolve foreign particles therein, washed with water and subsequently with percent nitric acid solution at room temperature and again with water. The aluminum workpiece thus pretreated was immersed in distilled water containing different quantities of ETHODUOMEEN (tradename for ethylene oxide adduct of fatty acid diamine) and heated at different temperatures and for different lengths of time as specified in Table 1 below.

EXAMPLE II The procedure of Example I was followed in pretreating an aluminum workpiece. The coating composition was also the same as in Example 1 except that triethanolamine was used in place of triethylamine. The pretreated aluminum workpiece was immersed in the coating composition for 20 minutes at different temperatures. The workpiece thus coated was pulled out,

TABLE 1 10 drained for 8 minutes, set for 8 minutes and heated at 180C for 30 minutes.

Color of Film TABLE 3 Temperature Time Amlne color of Film c C) (mmutes) 1% 5% 10% Temperature Amine 40 3 g 0.1% 0.5% 1.0%

35 1 2 2 1 40 2 l 0 6O 3 3 2 s o 1 1 1 20 e0 20 2 3 3 2 2 3 3 80 g g 5 The finished aluminum workpiece was subjected to 35 l 2 2 2 Erichsen test in which it retained the value of 100 for over 20 test hours. 5 0 0 0 0 90 5(5) 1 i EXAMPLE III The procedure of Example I was followed under the l 00 g 8 g g 8 conditions which are shown in Table 4 below.

0 0 0 0 TABLE 4 A 7 T Color of Note: The numbers 0-3 above represent the degrees mine 0 amp Time of color of the coated film as determined by naked n Film eye as follows: 35 Monopropylamine 0.l% 60 30 l Ethylenediamine 0.01% 60 20 1 0 C0101 Morpholine 0.3% 60 20 2 3-methox to l 'n 60 20 l l hght amber (15% y p w e Dimethylethanolamine 0.1% 60 20 l 2 amber 40 Ethylene oxide adduct of fatty acid 80 5 3 amine 5% 3 Clear amber Ethylene oxide adduct of fatty acid 60 35 3 diamine 5? The alummum workp1ece thus under-coated and col- Ethylene oxide adduct of coconut 40 20 3 ored was immersed in a coating composition identified ?*g ;g 60 20 2 l'l in Table 2 below. Th1s 1mmers1on was continued for l 0 minute at room temperature. The workpiece thus overcoated was pulled out, drained for 3 minutes, allowed to set for 8 minutes and thereafter heated at 180C for EXAMPLE IV 30 minutes to harden the coating, whereupon there was produced a continuous, uniform, colored film on the aluminum workpiece.

TABLE 2 Coating Composition Acrylic resin 25.8% Melamine resin 6.4% Triethylamine 3.2% Glycol l9. l% lsopropyl alcohol 30.2% Water 8.0% Surfactant 7.3%

The procedure of Example I was followed in pretreating an aluminum workpiece. The coating composition used in the instant Example was the same as in Example I except that the various amines listed in Table 4 were used in place of triethylamine. The workpiece was immersed in the coating composition at the temperatures and for the duration of times that are listed in Table 4. The coated workpiece was pulled out, drained for 3 minutes, set for 8 minutes and heated at C for 30 minutes. The finished workpiece exhibited the results of ductility test and color appearance which are comparable to those shown in Example lll.

It is to be noted that there can be obtained an excellent amber finish on coated surfaces of an aluminum substrate under controlled temperature conditions according to the invention. This is believably due to the fact that there is a peculiar relation between the speed at which aluminum is oxidized during the formation of boehmite and the speed at which aluminum is reduced by the activity of amine and that there is a certain range of temperatures at which the reduction of aluminum takes place preferentially over theoxidat ion thereof. It isto be further noted that amines if used in excess of the amounts herein specified tend to corrode an aluminum substrate and fail to produce a desired amber col- What is claimed is:

l. A process for producing a coating on an aluminum substrate comprising a coat of a resin which is derived from an originally water-soluble thermosetting which is an acrylic, an alkyd, a melamine, phenolic, urea and aminoalkyd resins or a mixture thereof, comprising cleaning said aluminum substrate with warm diluted caustic soda, immersing the aluminum at least for 5 minutes in an aqueous composition comprising 50 percent of at least one water-soluble thermosetting resin which is selected from the group consisting of acrylic, alkyd, melamine, phenolic, urea and aminoalkyd resins and 0.1 10 percent of an organic amine' selected from the group consisting of dimethylethanolamine, monoethanolamine, triethanolamine, mono-normal-propylamine, tetraethylenepentamine and ethylenediamine at 40 C and then allowing the thus coated aluminum surfaces to set, dry and harden at 200C over a period of 15 30 minutes.

2. The process according to claim 1 wherein said composition comprises an acrylic resin, a melamine resin 8 percent water and about 50 percent of at least one aliphatic hydroxy compound miscible with water.

3. The process according to claim 1 wherein the said composition comprises 25.8 percent of an acrylic resin, 6.4 percent of a melamine resin, 3.2 percent of triethylamine, l9.l percent of glycol, 30.2 percent of isopropyl alcohol, 8 percent water, 7.3 percent of a surfactant.

4. The process according toclaim 1 wherein said coating is amber colored. 

2. The process according to claim 1 wherein said composition comprises an acrylic resin, a melamine resin 8 percent water and about 50 percent of at least one aliphatic hydroxy compound miscible with water.
 3. The process according to claim 1 wherein the said composition comprises 25.8 percent of an acrylic resin, 6.4 percent of a melamine resin, 3.2 percent of triethylamine, 19.1 percent of glycol, 30.2 percent of isopropyl alcohol, 8 percent water, 7.3 percent of a surfactant.
 4. The process according to claim 1 wherein said coating is amber colored. 